Manufacturers of vehicles that employ internal combustion engines, more particularly diesel engines, are striving to reduce and control exhaust emissions and comply with current and future emission standards for the release of oxides of nitrogen (NOx), unburned and partially oxidized hydrocarbons (HC), carbon monoxide (CO), particulate matter, and other emissions, (i.e., hydrogen sulfide (H2S) and ammonia (NH3)). In order to reduce the previously mentioned emissions, diesel engines are typically operated with exhaust gas after-treatment systems.
Exhaust gas after-treatment systems typically include, but are not limited to, one or more after-treatment devices, such as oxidation catalysts, NOx abatement devices, diesel particulate filters (DPFs) and sulfur traps. These after-treatment devices generally require certain conditions to exist in the engine exhaust gas in order to perform optimally. For example, NOx abatement devices and oxidation catalysts, have a relatively narrow temperature window within which the devices activate, regenerate, or operate with high conversion efficiency. Some after-treatment devices require heating of the device to temperatures that are higher than those typically provided by the engine exhaust gases in order to achieve the desired operating temperature of the after-treatment device. One example of such a device is a diesel particulate filter (DPF).
Diesel particulate filters entrap particulates carried by a diesel engine exhaust flow, in operation, such diesel particulate filters accept exhaust flow at one end and trap particulates as exhaust gases diffuse through thin channel walls and exit out the other end. Continued particulate buildup in the diesel particulate filter is undesirable thus, it is necessary to clear the particulate buildup before the filter is obstructed.
Clearing of the particulate buildup is performed by a regeneration process wherein the temperature of the DPF is raised to a level sufficient to cause combustion and vaporization of the particulates captured by the DPF. Once the particulates are vaporized, the combustion products may be swept out of the filter by the exhaust stream.
In order to provide for localized heating to efficiently remove particulates from the filter the exhaust gas temperatures in the DPF must be increased. There are two primary regeneration events for a DPF: passive and active. During passive regeneration, exhaust gases reach sufficient temperatures to promote catalytic reactions that oxidize trapped soot. In active regeneration modes, the onboard engine control module forces the system to increase exhaust gas temperatures and/or regulate available oxygen content to either promote or halt a regeneration event. Regeneration events typically require exhaust temperatures between 570 and 650 degrees Celsius.